The nematode Caenorhabditis elegans has been adopted as a model organism for a variety of biomedical research applications. This organism offers many advantages for analysis, including the ability to study mutations in genes that are essential for viability. The long-term goal of this proposal is to provide a comprehensive genetic resource available to the biomedical research community as a computerized databank, and as a comprehensive collection of genetic stocks. The proposed five-year project will first generate and characterize a set of chromosomal balancers that would cover the entire genome. Balancers are chromosomal rearrangements that suppress recombination, allowing lethal mutations to be stably maintained in heterozygous stocks. At present, about 50% of the genetic map (with a total of 850 mapped loci) is covered by proven balancers. Another 30% of the map includes potentially useful rearrangements, and about 20% has no possible balancers as yet. The efficacy of uncharacterized rearrangements will be tested first, and additional rearrangements will be generated as needed. Secondly, this project will generate and characterize sets of overlapping deficiencies for each chromosome that would make up a moderately high resolution "mapping kit" for the genome. This will involve approximately 200 deficiencies per chromosome, and would vastly improve the alignment of the genetic and physical maps. Free chromosomal duplications also will be tested as balancers and used for mapping. This "cover the genome" project will provide a common resource for molecular biologists who want to generate lethal or non-lethal mutations in the region of a particular cloned gene, and it could constitute Phase I of a longer-term project Phase II, beyond the scope of the initial five-year period, would be to approach saturation of the genome by isolating and mapping lethal mutations defining almost every essential gene. Ultimately, the successful completion of Phase II would mean that the basic genetics of C. elegans would be "in the bank" and available to any investigator who wanted to look at mutant characteristics corresponding to any gene in the C. elegans genome sequence database. An alternative to collecting a large number of lethal mutants would be to develop gene disruption procedures. This will require a method to target transforming DNA to the homologous site within the genome. Hence, an investigation of DNA integration by homologous recombination is proposed as a component of Phase I.